1. Field of the Invention
The present invention relates to an overhead projector comprising light sources, a reflection mirror that reflects a light from one of said light sources toward a reflection type light collecting lens and a projection lens that projects a light from the light collection lens, while housing them in a cabinet.
2. Description of the Prior Art
Conventional overhead projectors in this type of structure, as known in the prior art, are shown in FIGS. 4 and 5. In FIGS. 4 and 5, numerals represent various devices as follows: 1 and 2 for light sources, 3 for a first reflection mirror that reflects a light of said light source 1 and 2 toward a light collection lens 4 of a reflection type and 5 for a projection lens that projects a light of the light source 1 or 2 reflected by the light collection lens 4 onto a screen 7 via a second reflection mirror 6. Said light sources 1 and 2, the first reflection mirror 3 and the projection lens 5 are housed in a flat, rectangular parallelepiped overhead cabinet (hereinafter referred to as a cabinet) 8.
Or explicitly, one 1 of the 2 light sources 1, 2 is mounted to direct its light axis k toward a center portion of a mirror surface of the first reflection mirror. The other light source 2 is mounted parallel to and immediately in the side of the light source 1.
The light source 1 is constructed slidably aside (direction a) toward a position shown by a chain line, for escaping. The light source 2 is constructed so that it can move to the position of the light source 1 after it has escaped, by sliding it aside (direction b) in the same way.
In addition, the light source 1, the first reflection mirror 3 and the projection lens 5 are mounted in a row on the center lines in the lateral and height directions of the cabinet 8.
Since such a composition as described above is employed, if a light source 1 burns during the operation of the projector, it is possible to move the light source 1 to the position of a chain line while moving the other light source 2 to that place where the light source 1 was.
However, with a conventional overhead projector known in the prior art, light source 1, 2 are arranged parallel in the direction w in the cabinet 8 while making a light source 1 escape into the position of the chain line and moving the other light source 2 to the place where the light source 1 was located. Therefore, there are the following problems :
(1) The width W of the cabinet 8 must be as large as three light sources 1 are arranged laterally in a row. Consequently, a larger cabinet 8 is required and cannot satisfy the requirement for a more compact structure.
(2) When a light source 1 burns and must be replaced with the other light source 2, it is required to move them to the position of a chain line and the place that was occupied by the light source 1, respectively in manual operation. However, the light source 1 is heated up so high as the operator cannot replace it immediately. Therefore, the use of the projector has to be interrupted until light sources 1, 2 are cooled down.